1. Field of the Invention
The present invention relates to a flexible membrane weir capable of adjusting a water level which is normally called "rubber weir". More particularly it relates to a mount structure for mounting such membrane weir onto a dam crest.
2. Description of the Prior Art
One example of the heretofore known structure for mounting a rubber weir onto an existing dam crest is shown In FIG. 6. Referring to this figure, a dam crest 02 having a crest surface 02a of arc shape in cross-section is formed on a river bed between banks 01 on the respective sides of a river.
A pedestal 04 having its top surface 04a formed of a horizontal plane extending horizontally from a top line t (dash-dot line) of the crest surface 02a to the upstream side, is formed over the entire length in the widthwise direction of the river bed. A superimposed free end of a twice-folded rubber membrane 03 is placed on the top surface 04a of this pedestal 04, and it is fixed to anchor bolts 06 as pressed by a fixing metal 05.
Since the free end on the upstream side of the rubber membrane 03 is fixed onto the horizontal top surface 04a of the pedestal 04, the mount structure of the rubber membrane 03 becomes similar to that in the case of mounting it onto a planet river bed. Thus, when the rubber membrane 03 falls, it can fall without its toe of slope 03a forming excessive protrusions on the top surface 04a of the pedestal 04 nor on the face of slope 01a of the bank 01. As a result a fitting property of the rubber membrane 03 becomes good, hence smooth flow of river water can be realized, and an excessive force would not act upon the rubber membrane 03.
However, since the configuration of the crest 02 changes over the entire length in the widthwise direction of the river bed as a result of provision of the pedestal 04, a coefficient of discharge would lower by about 10%. In addition, since the pedestal 04 extends over the entire length in the widthwise direction of the river bed, a cost of construction as well as a period of construction would be increased.